#1412

[@NikiBretschneider]

6:52 It is not 8 bits in one direction and 8 bits in other direction, it is 8 LEVELS in each direction, which means is 3 bits ( log(8)/log(2) )in one direction and 3 bits in other direction. At the moment of sampling, your signal can touch only ONE of that levels, but you can have multiple 1 and 0 in one symbol. In fact, the QAM64 carries 64 different levels (8×8 constelation) per symbol, which is 6 bits per symbol ( log₂(64) ). The begining of that explanation was perfectly correct, but then it slipped from 8 levels to 8 bits, which is typical mistake when it comes to these modulations.

[@Edisson.]

Nikky, you got angry somehow 😁 Přeji ti krásný den 😉 Tom

[@sethalump]

Thanks for breaking this down in a visual manner

[@750kv8]

This is such a simple and clear explanation and demonstration, thankyou! the dot pattern display i believe is essentially a vectorscope

[@tswtx]

We use QAM modulation on Dense Wave Division Multiplexing optical networks where the SNR is high enough. The baud rates are incredible... over 100 gigabaud on newer transponders.

[@aduedc]

Thanks, I learned how to view constellation diagram on oscilloscope.

[@joeteejoetee]

NICE explanation and Video!

[@cablemedic207]

So the same test on your cable tv line Most providers now are using 256 QAM on their forward digital channels It’s always fun reading constellations in the field trouble shooting MER/BER issues , aka tiling pictures..

[@Edisson.]

Hello, very informative video, I happened to notice that Siglent also offers a similar board under the name STB - 3 Nice day 🙂 Tom

[@juliohormilla3862]

I don't think the STB-3 has QAM

[@stevecoats4869]

Hi. Great video and learnt something new! Such a shame you did not single shot the xyz mode to shoe the different data.

[@jasonschlencker8108]

That is very interesting.

[@jerrydaugherty3781]

Like to see operation of Quadrature decoder putting it back into hard data.

[@mr1enrollment]

Well done.

[@LiraLab]

That`s amazing! I got an MSO5354 and I`ll try that!!

[@christianzazzali2720]

I couldn't find a contact in the "about" I posted photos in my channel

[@BaldurNorddahl]

Something is missing. You should see if you can modulate that I/Q signal on a carrier and then decode the result on the Siglent spectrum analyzer. The I/Q signal on a carrier should generate something that is both amplitude and phase modulated.

[@IMSAIGuy]

you are thinking of the RF domain where the Q signal is moved 90 deg during the conversion.

[@BaldurNorddahl]

@@IMSAIGuy yes of course. That is the whole point of IQ after all. The part of QAM shown in the video is actually what you have either before rf modulation or after demodulation. It becomes just one RF signal, not two separate signals. I think that is an important point to understand what QAM is all about. So the I signal is modulated to a RF carrier, then the Q signal is modulated to a RF carrier of same frequency but 90 degree phase difference and finally the two carriers are added. This is the final QAM signal that actually can be transmitted on coax to your TV or on the air as a radio wave to your cell phone etc. My siglent spectrum analyzer has a QAM decoding module. Maybe your does too. I am not sure as mine is the ssa3032x-r fully unlocked. If you have it, it would be a great video to show decoding of RF modulated QAM.

[@IMSAIGuy]

@@BaldurNorddahl the 'plus' version of the SA has that, mine does not

[@NikiBretschneider]

This is what these simple presentations typically lack of - the basics. Why there are two (I and Q) signals, why they are mixed with π/2 phase shifted LOs, why there is that π/2 phase shift, where it came from etc., which typically makes this theme completely non-understandable. That lecture should begin with the quadrature mixers, which was widely used to generate SSB signals, especially in microwave oriented constructions, giving the strong base to understanding all that following vector oriented stuff. But this would be long, it would require some kind of concentration and math skills and I don't think this is what typical youtube viewer wants. They don't want to understand that topic, they just want to watch something having fun.

[@IMSAIGuy]

There are plenty of hard core engineering channels. Lots of professors in India who will teach you IQ modulation. I try to fill the gap at the lower end for those who will never be engineers and just enjoy building stuff and learning along the way.

[@RobRoschewsk]

How does this relate to phase shift keying? Is that an alternate technique to get multiple bits per cycle?

[@IMSAIGuy]

MODULATION BITS PER SYMBOL SYMBOL RATE BPSK 1 1 x bit rate QPSK 2 1/2 bit rate 8PSK 3 1/3 bit rate 16QAM 4 1/4 bit rate 32QAM 5 1/5 bit rate 64QAM 6 1/6 bit rate

[@NikiBretschneider]

The main difference between the n-QAM and n-PSK signal lays in different constellation diagram. n-PSK has n points spread on a circle, but in the n-QAM they are spread into the square. This results in a fact, that n-PSK affects only the phase of the resulting signal, it has no AM portion, which means that your signal path does not require to be linear (similar to FM or ΦM). QAM contains amplitude portion, which requires linearity (which is typical pain in the ass when it comes to RF PAs), but on the other hand, the error detector, which is crucial part of demodulator controlling all that phase and gain loops, is much simpler to implement, which is a great advantage when it comes to high speed data. Both systems use multiple levels to encode multiple bits into one symbol, so the symbol rate (this is how many changes of that signal happens per second) is different from bit rate. And there is also one more similarity. If you think about 4-QAM. Yes it is exactly the same modulation scheme as a QPSK, but this is the point where all that similarity ends.

[@sbelectronicaindustrial6652]

Nice Video, good information...!!

[@chiraldude]

That's fun but what about the case where this goes into an antenna and you are trying to demodulate in a radio receiver? There's no clock signal so demodulating becomes really fun!

[@IMSAIGuy]

fun: opg.optica.org/oe/fulltext.cfm?uri=oe-22-13-15376&id=294065

[@johnwest7993]

You could come closer to reading the leading edge of the clock if you added a circuit to narrow the Z axis pulse. I suppose that would make the display dimmer, but it should give you a more accurate image of the data.

[@luckyfarru]

Great content Is there any online Udemy or similar course that u can recommend to gain better understanding for beginners

[@ghlscitel6714]

Is QAM allowed in radio amateur bands?

[@IMSAIGuy]

yes

[@ghlscitel6714]

@@IMSAIGuy Thanks. So if we assume an efficiency of around 2 bits per Hz (QAM256), with a 5 kHz bandwidth we could transfer 10 kbit/s in 1 HAM channel. Would be nice... Has anyone tried that already?

[@IMSAIGuy]

www.sigidwiki.com/wiki/Category:Amateur_Radio

[@ghlscitel6714]

@@IMSAIGuy Thank you!

[@zyeborm]

Totally unrelated but kicad 7 came out a few days ago and I think it has the drag mode you wanted in it now. Check the change log but from the pictures in it I think it did the thing. Couldn't find the video where you asked about it so replying here sorry.

[@IMSAIGuy]

nope, just downloaded and tried

[@byronwatkins2565]

As a personal preference, I would put the dots in the centers of the squares.

[@johnprouty6583]

That’s the way I’ve always seen it done. It gives you an idea of potential error when the point falls outside the assigned square.

[@dixsusu]

@@johnprouty6583 In other words: Error Vector magnitude !

[@chronobot2001]

I was hoping to see a practical application of this. As it is, I don't know what this is useful for.

[@IMSAIGuy]

QAM is used extensively as a modulation scheme for digital telecommunication systems, such as in 802.11 Wi-Fi standards.

[@christianzazzali2720]

In community tab

[@DAVIDGREGORYKERR]

Can you not the MOTOROLA C-QUAM chips one for encoding and decoding, QAM is nothing new as MOTOROLA had a set of chips out that facilitated stereo over Medium Wave frequencies as well as Long Wave frequencies and possibly the SW bands as well.

[@jbrown468]

Awesome video!